AIDS is a viral disease, and clinical progression is associated with increased viral burden. Accurate assessment of HIV-1 level in vivo will be critical for monitoring treatment efficacy. Our laboratory was the first to develop quantitative cultures which can determine the infectious titers of HIV-1 in the plasma and peripheral blood mononuclear cells of patients. Furthermore, we have utilized these end-point-dilution assays to demonstrate the presence or absence of in vivo efficacy of antiviral agents. In the past two years, quantitation of HIV-1 DNA in clinical samples by PCR methods has also been achieved in our laboratory. This quantitative PCR technique has permitted the detection of fluctuations in HIV-1 load in the patients encountered by us. We now propose to refine these quantitative techniques so that we can accurately and quantitatively measure infectious HIV-1 and its nucleic acids in a number of clinical specimens.